1. Field of the Invention
This invention relates to digital RF transmitters and transceivers, and more particularly to digital transmitter and transceiver systems capable of simultaneously servicing multiple channels.
2. Description of the Related Art
There are a number of areas in which multiple channel transmission is required, including applications which call for different modulation formats and bandwidths. For example, commercial avionics requires both air-to-air and air-to-ground communication and data links for the transmission of voice and data, a radar altimeter which measures the reflection of a radio signal from the ground to determine the distance from the plane to the earth's surface, and an S-mode transponder transceiver that responds to a ground radar signal and returns a signal with aircraft identification, airspeed, heading, and altitude information for air traffic control operations.
With current technology, each of these communication links requires a separate transmitter. The signals may be generated digitally, but are converted to analog format and amplified for transmission. The analog components, including the analog-to-digital converter (ADC) and digital-to-analog converter (DAC), are the most costly elements; providing these elements separately for each different transmission channel multiplies the overall cost. In addition, providing a separate transmitter for each different channel increases the size, weight and power requirements of the overall communications system.